A video and/or audio multipoint conference is a more and more important communication manner. In the current multipoint conference networking manner, Multipoint Control Unit (MCU) cascading is a quite convenient and practical networking mode. A cascaded conference refers to a conference networking mode of a large conference formed among multiple MCUs through calls, which is in a tree structure. An MCU at an upper layer is referred to as an upper level MCU, and an MCU at a lower layer is referred to as a lower level MCU. Upper levels and lower levels are relative.
When a cascaded conference is formed, a call may be initiated between upper and lower level MCUs, and a channel may be established to transmit a code stream of a site.
A call can at most only negotiate two channels used for transmitting a site image (video) (separately used for receiving an image code stream and sending an image code stream), and/or two channels used for transmitting site audio, and/or two channels used for transmitting site data (all these channels are referred to as cascade channels), so a lower level MCU can at most only send an image code stream of a site, and/or an audio code stream of a site, and/or a data code stream of a site to an upper level MCU at the same time. If the upper level MCU needs to obtain image code streams of multiple sites, and/or audio code streams of the multiple sites, and/or data code streams of the multiple sites of a lower level MCU at the same time, they can be obtained only in a polling manner.
It should be noted that, in a conventional cascaded conference, only the above fixed cascade channels may be negotiated, multi-cascade channels mentioned below are several similar channels established besides the cascade channel.
In the prior art, the manner for transmitting multiple site code streams between upper and lower level MCUs is as follows (taking an image code stream of a site as an example):
1) Before a cascaded conference is held, the number of multi-cascade channels between upper and lower level MCUs that will be used in the conference is determined, for example, 3.
2) In a process of holding the cascaded conference, an upper level MCU initiates a call with a lower level MCU additionally according to the number of multi-cascade channels specified before the conference, and the specified number of the multi-cascade channels is the number of calls that will be initiated.
3) In the conference, if the upper level MCU needs to watch images of multiple sites on the lower level MCU, the lower level MCU may use a channel established by the additional calls to send the images of the multiple sites. Likewise, a multi-cascade channel also can send an image code stream of a site only.
With the technology, multiple site images can be transmitted between upper and lower level MCUs, but the technology has the following technical drawbacks:
1. The number of multi-cascade channels must be specified before a conference. If in a conference, the number of sites on a lower level MCU that are expected to be watched by an upper level MCU exceeds the specified number of multi-cascade channels, not all sites expected to be watched can be watched.
2. The number of multi-cascade channels specified before a conference is the number of additional calls generated in a conference creation process. If the multi-cascade channels are not used in the conference, the calls still exist, occupy system resources of an MCU such as call resources, and cannot release the resources.